1. Field of the Invention
This invention relates to granulating and coating techniques, and more particularly to techniques wherein a powdery or granular material is put in a rotary drum rotatable about substantially horizontal shaft and the rotary drum is rotated so as to perform granulating and/or coating, drying and so on of the powdery or granular material.
2. Related Art Statement
As the granulating and coating techniques of the type described, there has been known techniques wherein a rotary drum, which is also called as a coating pan, is rotated about a horizontal shaft and a gas such for example as a hot air is fed into the rotary drum and discharged therefrom, whereby pharmaceuticals, food products, chemical products and other various powdery or granular materials are subjected to granulating and/or coating.
In that case, such a technical problem is posed that how effectively the powdery or granular material in the rotary drum is agitated and mixed so as to perform a desired granulating and/or coating efficiently and uniformly.
To solve this problem, the provision of a baffle means as an obstacle in the rotary drum is proposed (Examined Patent Publication No. 52-10665).
Now, as shown in FIG. 3, since a rotary drum D in the prior art has a circular construction in cross-section, there is a difficulty that a powdery or granular material M, which should be brought to the advanced position in a rotating direction along with the rotation of the rotary drum D, slips on the inner wall surface of the rotary drum D, so that the powdery or granular material M cannot be tumbled satisfactorily.
Furthermore, when slips are extreme, the baffle means contributes as a resistance to enhance slips and even obstructs agitating of the material.
Particularly, in a large-sized apparatus, due to slips, the powdery or granular material may not be rasied even to a position of a baffle means B located at the advanced position in a rotating direction R of the rotary drum D. Thus, although the baffle means is provided in the rotary drum D, it may not be possible to obtain the desired functional effect.
It goes without saying that, even with a small-sized apparatus, due to slips, a layer of the powdery or granular material M may not be tumbled, staying at a predetermined state so that the agitating and mixing effects through the baffle means B are small.